Hi shane. Do something like this:
var newValues = new GradeBookItemEntity();
newValues.Fields[(int)GradeBookItemFieldIndex.PercentValue].SetExpression(
new DbFunctionCall("CASE WHEN {0} IS NULL THEN NULL ELSE {0} / 12 END",
new object[] { GradeBookItemFields.RecordedGrade }));
var filter = new PredicateExpression(GradeBookItemFields.AssignmentId == 562645);
var rowsAffected = new GradeBookItemDAO().UpdateMulti(newValues, null, filter);
You also could use a GradeBookItemCollection istead of GradeBookItemDAO. This is explained here in the docs....